Field of the Invention
The present invention relates to a tilting oxygen converter provided with a suspension system of the container of the converter connecting said container to a support ring.
State of the Art
The main object of an oxygen converter is to convert the cast iron produced in the furnace into raw liquid steel, which may be subsequently refined in the secondary steel production department.
The main functions of the oxygen converter, also known as B.O.F. (Basic Oxygen Furnace), are to decarburize and remove phosphorous from the cast iron and to optimize the temperature of the steel so that further treatments may be carried out before casting with minimum heating and cooling of the steel.
The exothermal oxidation reactions which are generated in the converter produce a great deal of thermal energy, more than that needed to reach the established temperature of the steel. This extra heat is used to melt scrap and/or additions of ferrous material. The B.O.F. container, being substantially a furnace, is also subject to high thermal expansions.
The converter consists of a container, defining the reactor and having a substantially cylindrical shape, supported by a support ring, surrounding the container and appropriately distanced therefrom, provided with two diametrically opposite supporting pins, all supported by two supports anchored to the ground. The rotating control of the container is fitted onto one of the two supporting pins.
An example of oxygen converter of the prior art is described in WO2008/092488A1. The container of such a converter is supported by means of an outer support ring and a plurality of suspension elements connecting said container to said support ring, the suspension elements being restrained at a first end to the container and at a second end to the support ring.
First suspension elements are formed by packs of lamellae which are arranged in a distributed manner under the support ring, considering the converter in its upright position with the loading mouth facing upwards. One end of the packs of lamellae is fixed onto a lower surface of the support ring; the other end of the packs of lamellae is fixed to a lower frustoconical portion of the container. In such a configuration, the packs of lamellae are arranged inclined by an angle of approximately 20-25° with respect to a respective vertical plane containing the longitudinal axis defined by the converter.
Second suspension elements are formed instead by pendulum rods, which are hinged at one end to the support ring and at the other end to the container. Considering the conveyor in its upright position with the loading mouth facing upwards, such pendulum rods are arranged horizontally at the two supporting pins above and under the support ring.
Disadvantageously, in the packs of lamellae made and arranged in the manner described above, excessively concentrated loads are created at the fastening points of the lamellae to the support ring and to the structure of the container of the converter. In particular, such packs of lamellae so configured are transversally rigid and do not allow the flexion and torsion of the lamellae themselves, and thus the redistribution of the stresses when the converter is turned by 90° from its vertical position to carry out the step of tapping.
Furthermore, the different thermal expansion of the container and of the support ring determines high concentrated loads in the fastening points of the lamellae due to the fact that the attachment of the lamellae themselves on the container tends to shift because it expands more, while the attachment of the lamellae on the support ring tends to remain in position because it expands less.
Another example of oxygen converter of the prior art, similar to that disclosed in WO2008/092488A1 (FIG. 1a), is described in US2012/0223107A1 (FIG. 3).
A further example of oxygen converter of the prior art is disclosed in GB2492735. In this converter the converter vessel or container is secured to the trunnion ring by means of a plurality of connecting elements, and each connecting element is rigidly secured by means of its opposing ends to the underside of the trunnion ring at one end and to the converter vessel at the other end. Each connecting element comprises precisely one lamella which is shielded from the converter vessel by means of a protective element that is connected by means of its opposing ends both to the converter vessel and to the trunnion ring, but only one of these ends is rigidly connected either to the trunnion ring or to the converter vessel. Therefore said protective element does not itself have any bearing function. Each lamella defines an own laying plane that is clearly different from the laying plane of the adjacent lamellae, being each lamella distanced from the adjacent ones and fixed in an area of the converter angularly distanced from the fixing areas of the adjacent lamellae. Moreover each lamella has respective distinct fastening supports. Even if this solution allows to slightly reduce the concentrated loads at the fastening points of the lamellae, it is still felt the need to make a tilting converter which allows to better overcome the aforesaid drawbacks.
The centering between container and support ring is also important to suitably allow deformations or thermal expansions of the container caused by the high temperatures reached during the refining process.